Method and apparatus for sharing radio frequency spectrum in a radio frequency communication system

ABSTRACT

A radio frequency communication system is coupled to a telephone network having automatic number identification (ANI) capabilities for communication thereover. The radio frequency communication system includes at least one relocateable base station (115) which shares a radio frequency channel with stationary communication devices for communicating over predetermined geographic areas. The radio frequency communication system further includes a service center (125) which, in response to a call from a base station (115), receives from the telephone network information indicative of at least a portion of a telephone number from which the base station (115) is calling. The service center (125) determines therefrom whether the base station (115) is located within any of the predetermined geographic areas. When the base station (115) is not located within any of the predetermined geographic areas, the service center (125) transmits an authorization signal over the telephone network indicating that the base station (115) is authorized for radio frequency communication over the shared radio frequency channel.

This is a division of application Ser. No. 08/064,306, filed May 20,1993, now U.S. Pat. No. 5,422,930.

FIELD OF THE INVENTION

This invention relates in general to radio frequency communicationsystems, and more specifically to a radio frequency communication systemin which the radio frequency spectrum is shared.

BACKGROUND OF THE INVENTION

Radio frequency communication systems are typically allocated a radiofrequency spectra over which system users transmit and receiveinformation. As the number of users of radio frequency communicationsystems increase, the usable radio frequency spectra is becomingincreasingly scarce. In many regions of the United States, for example,the radio frequency spectrum set aside for cellular telephone users hasalready become saturated to such an extent that cellular subscribersmust often wait for an available radio frequency channel. As the numberof cellular subscribers increases, users will experience increasinglylonger delays in obtaining an available channel.

In addition to existing systems, such as cellular systems, new two-waycommunication systems are planned which will require additional radiofrequency spectrum. As these new systems are implemented, subscribers tothe new systems will further crowd the usable radio frequency spectra.

One method for more efficiently utilizing the currently available radiofrequency spectra is to share allocated radio frequencies between usersof different radio frequency communication systems. A problem with thismethod is that the users of one communication system may sometimesinterfere with the users of another communication system sharing thesame radio frequencies. Accordingly, some known frequency sharingschemes allocate a radio frequency channel to one or more stationaryusers located in a first geographic area. The same radio frequencychannel is then allocated to other stationary users located in a secondgeographic area that is far enough away from the first geographic areato prevent interference between the users of the two different systems.This frequency sharing scheme, however, is only workable forcommunication systems in which the users are stationary and do not roaminto areas wherein interference will occur between users of thedifferent systems.

Thus, what is needed is a frequency sharing scheme for mobile users thatprevents interference between users of different communication systemssharing the same radio frequency channels.

SUMMARY OF THE INVENTION

A base station, in a radio frequency communication system, is capable ofbeing relocated among a plurality of geographic regions forcommunicating over a radio frequency channel. The base station sharesthe radio frequency channel with stationary communication devices overpredetermined geographic areas and is capable of accessing a telephonenetwork to communicate with a service center which authorizes use of theradio frequency channel by the base station.

The base station includes a memory for storing a first predeterminedtelephone number of the service center and accessing circuitry forcalling the first predetermined telephone number over the telephonenetwork. The accessing circuitry receives, in response thereto, anauthorization signal over the telephone network. The authorizationsignal indicates that authorization of radio frequency communicationover the radio frequency channel is allowed in response to the servicecenter determining that the base station is not located in one of thepredetermined geographic areas of the stationary communication devices.The service center determines the location of the base station basedupon a telephone number from which the base station places a call to theservice center.

The base station also includes a transceiver for transmitting andreceiving communications over the radio frequency channel in response toreception of the authorization signal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a radio frequency communication systemwhich shares a radio frequency channel with stationary communicationdevices in accordance with a preferred embodiment of the presentinvention.

FIG. 2 is an electrical block diagram of a relocateable base stationincluded within the radio frequency communication system of FIG. 1 inaccordance with the preferred embodiment of the present invention.

FIG. 3 is an electrical block diagram of a service center forauthorizing the relocateable base station of FIG. 2 in accordance withthe preferred embodiment of the present invention.

FIG. 4 is a flowchart depicting the operation of the controller includedwithin the base station of FIG. 2 in accordance with the preferredembodiment of the present invention.

FIG. 5 is a flowchart depicting the operation of the microprocessorincluded in the service center of FIG. 3 in accordance with thepreferred embodiment of the present invention.

FIG. 6 is an electrical block diagram of a relocateable base station inaccordance with a first alternate embodiment of the present invention.

FIG. 7 is a flowchart depicting the operation of the controller includedwithin the base station of FIG. 6 in accordance with the first alternateembodiment of the present invention.

FIG. 8 is an electrical block diagram of a relocateable base station inaccordance with a second alternate embodiment of the present invention.

FIG. 9 is a flowchart depicting the operation of the controller includedwithin the base station of FIG. 8 in accordance with the secondalternate embodiment of the present invention.

FIG. 10 is an electrical block diagram of a relocateable base station inaccordance with a third alternate embodiment of the present invention.

FIG. 11 is an electrical block diagram of a service center for use withthe base station of FIG. 10 in accordance with the third alternateembodiment of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

FIG. 1 is an illustration of a radio frequency (RF) communication systemfor sharing, in accordance with a preferred embodiment of the presentinvention, a predetermined RF channel with stationary point-to-pointcommunication devices, such as microwave point-to-point stations 105that have highly directional antennas. Each pair of microwave stations105 communicate over predetermined geographic areas 110 in a manner thatis well known to one of ordinary skill in the art. It will beappreciated that the predetermined geographic areas 110 depend in parton various factors including the output power of the transmitters at therespective locations, the height of the antennas, the direction of theantennas, the directional selectivity of the antennas, the surfacefeatures of the geographic areas 110 between the microwave stations 105,and the sensitivity of the receivers at the microwave stations 105.

Because the RF channel over which the microwave stations 105 communicateis utilized only over the predetermined geographic areas 110, regionssurrounding the predetermined geographic areas 110 can be used tocommunicate on the same RF channel without interfering with themicrowave stations 105. As a result, an RF communication system canshare the RF channel if devices included therein do not interfere withthe microwave stations 105. In other words, the devices included withinthe RF communication system are excluded from transmitting on the radiofrequency channel within the predetermined geographic areas 110,hereafter referred to as "exclusion zones".

The RF communication system which shares the RF channel preferablyincludes a plurality of base stations 115 which are relocateable, i.e.,which can be easily moved from one geographic region to another. Thebase stations 115 utilize the RF channel to communicate with a pluralityof mobile units, such as portable telephone handsets 120. The portablehandsets 120 may be, for example, handsets utilized in a CT-2 (secondgeneration cordless telephone) communication system. As mentioned above,the base stations 115 and the portable handsets 120 preferably do notcommunicate while located within the exclusion zones utilized by themicrowave stations 105, thereby preventing interference between the RFcommunication system and the microwave stations 105.

The RF communication system further comprises a service center 125,which is coupled to each of the base stations 115 by a telephonenetwork, e.g., the public switched telephone network (PSTN) 130, havingautomatic number identification (ANI) capabilities, a feature which iswell known to one of ordinary skill in the art. The service center 125communicates over the PSTN 130 with each base station 115 to determinewhether the base station 115 has been relocated to a geographic regionin which its transmission range, i.e., coverage area, is encompassed byor overlapping an exclusion zone. When the base station 115 isdetermined to be located in a non-interfering geographic region, theservice center 125 transmits a first authorization signal to the basestation 115 authorizing RF communication over the RF channel. When,alternatively, the base station 115 is located such that interferencewith a microwave station 105 could result, the service center 125transmits a second authorization signal which prevents the base station115 from communicating over the shared RF channel.

In this manner, the shared RF channel is efficiently utilized becausethe base stations 115 which share the RF channel are able to relocate toany geographic region wherein the RF transmission range does not overlapan exclusion zone. As a result, a base station user can convenientlyrelocate his assigned base station 115 when necessary, as long as therelocated base station 115 does not interfere with microwave stations105 using the same RF channel. The RF communication system thereforeprovides for advantageous relocation of the base stations 115, unlikemany prior art systems in which the location of a transmitting basestation was fixed.

Referring next to FIG. 2, an electrical block diagram of a relocateablebase station 115 is depicted. In accordance with the preferredembodiment of the present invention, the base station 115 comprisesantennas 205 configured to receive and transmit RF signals over theshared RF channel. The antennas 205 are coupled to RF transceivers 210for encoding and decoding the communicated RF signals in a manner wellknown to one of ordinary skill in the art. The base station 115 furthercomprises a controller 215, which may, for example, be a microcomputer.Alternatively, the controller functions may be performed by hard-wiredlogic capable of performing equivalent operations. The controller 215preferably includes a central processing unit 220 for controlling theoperation of the base station 115. Additionally, the controller 215includes a first memory, such as a random access memory (RAM) 225, fortemporarily storing variables derived during operation of the basestation 115 and a second memory, such as a read only memory (ROM) 230,for storing subroutines executed by the CPU 220 during operation of thebase station 115.

Preferably coupled to the controller 215 is a clock 235 for generatingreal time values and a dual-tone, multi-frequency (DTMF) device 240which is capable of both encoding and decoding DTMF signals. The DTMFsignals are received from and, at the direction of the CPU 220, providedto a telephone interface 245 for accessing the PSTN 130 (FIG. 1) orother telephone network. Preferably, the telephone interface 245 ismonitored by monitoring circuitry 250, which may be internal to thecontroller 215. The monitoring circuitry 250 is coupled to the CPU 220for transmitting thereto a signal when the telephone interface 245 isdetermined to be disconnected from the PSTN 130.

According to the present invention, the telephone interface 245 includesa conventional telephone cord (not shown) for coupling to conventionaltelephone sockets. When the user of the base station 115 desires torelocate the base station 115, the telephone cord is unplugged from afirst socket, thereby disconnecting the telephone interface 245 from thePSTN 130, and later plugged into a second socket to reconnect thetelephone interface 245 to the PSTN 130. In this manner, the user caneasily carry a base station 115 from one location to another and bereasonably assured that the base station 115 can be coupled to the PSTN130 without complex adapters or connectors.

It may be appreciated by one of ordinary skill in the art that the basestation 115 can be implemented, for example, through use of aconventional private branch exchange (PBX) coupled to conventional RFtransceivers 210 and antennas 205, preferably by dedicated wirelines. Inthis situation, the transceivers 210 and antennas 205 would bephysically separated from the other circuitry, e.g., the controller 215,clock 235, DTMF device 240, and telephone interface 245, which would beincluded in or closely associated with the PBX. Therefore, when the PBXand associated transceivers 210 and antennas 205 were relocated, the PBXwould, as described above, initiate a call to the service center 125 toreceive an appropriate authorization signal.

FIG. 3 is an electrical block diagram of the service center 125 which iscoupled to the base station 115 through the PSTN 130. The service center125 comprises a telephone port 305 for coupling to the PSTN 130 to allowcommunication thereover and a DTMF device 310 capable of encoding anddecoding telephone signals, such as ANI information generated by thePSTN 130, communicated over the PSTN 130. The service center 125 furthercomprises processing circuitry, e.g., a microprocessor 315, which maybe, for example, an MC68HC05 microcomputer manufactured by Motorola,Inc. of Schaumburg, Ill. Further included in the service center 125 is amemory 320 coupled to the microprocessor 315 for storing first andsecond authorization codes which are encoded by the DTMF device 310 andtransmitted from the telephone port 305 as first and secondauthorization signals indicating, respectively, that RF communicationover the RF channel is allowed or denied to the base station 115. Thecorrect one of the first and second authorization codes is selected fortransmission by reference to a database 325 coupled to themicroprocessor 315. The database 325 is preferably utilized to store alisting of all telephone numbers of locations, including locationsincluded within the exclusion zones, wherein the base station 115 couldinterfere with the microwave stations 105. The telephone numbers can beupdated through use of a data entry device 330.

With reference to FIG. 4, a flowchart depicts the operation of the basestation controller 215 (FIG. 2) in accordance with the preferredembodiment of the present invention. At step 405, the monitoringcircuitry 250 monitors the telephone interface 245, and the CPU 220monitors the time values generated by the clock 235. When, at step 410,the telephone interface 245 is determined to be disconnected from thePSTN 130 (FIG. 1), the CPU 220 consults the RAM 225 to determine, atstep 412, whether a disconnect flag 415 (FIG. 2) is set, indicating thatthe telephone interface 245 has been previously disconnected from thePSTN 130. When the disconnect flag 415 is already set in the RAM 225,the telephone interface 245 and the time values continue to be monitoredat step 405. When the disconnect flag 415 is not set, the CPU 220 sets,at step 420, the disconnect flag 415 in the RAM 225.

When, at step 410, the telephone interface 245 is determined to becoupled to the PSTN 130 and, at step 425, the disconnect flag 415 is setin the RAM 225, the CPU 220 clears, at step 430, the disconnect flag415. Subsequently, the CPU 220 retrieves, at step 435, the telephonenumber 440 (FIG. 2) of the service center 125 which is stored in the ROM230.

When, at step 410, the telephone interface 245 is determined to becoupled to the PSTN 130 and, at step 425, the disconnect flag 415 is notset, operation of the controller 215 resumes at step 405 unless, at step445, the time value generated by the clock 235 is equivalent to a"call-in" time value 450 (FIG. 2) stored in the ROM 230. In this case,the CPU 220 also retrieves, at step 435, the telephone number 440 of theservice center 125 from the ROM 230.

Subsequent to the telephone number 440 being retrieved, at step 435, theCPU 220 provides, at step 455, the telephone number 440 to the DTMFdevice 240 one digit at a time for encoding thereby into a telephonesignal, which is transmitted to the PSTN 130 to call the service center125. As mentioned above, the PSTN 130, which has ANI capabilities,provides the service center 125 with at least a portion of the telephonenumber from which the base station 115 is calling, in response to whichthe service center 125 transmits one of two authorization signals overthe PSTN 130.

The CPU 220 receives the decoded authorization signal, i.e., theauthorization code, at step 460, and determines, at step 465, whetherthe received authorization code is equivalent to the first or the secondauthorization code 470, 475 (FIG. 2) stored in the ROM 230. When thereceived authorization code is equivalent to the first authorizationcode 470, indicating that communication over the RF channel is allowed,the transceivers 210 (FIG. 2) are enabled, at step 480, and RFcommunication with handsets 120 (FIG. 1) near the base station 115proceeds in a manner well known to one of ordinary skill in the art.

When the received authorization code is equivalent to the secondauthorization code 475 (FIG. 2), indicating that authorization for RFcommunication has been denied, the CPU 220 disables, at step 485, thetransceivers 210, thereby preventing RF transmissions that couldinterfere with communication between the microwave stations 105 (FIG.1). Thereafter, the call to the service center 125 over the PSTN 130 isterminated at step 490.

According to the above described embodiment, the base station 115 callsthe service center 125 for authorization when the telephone interface245 is coupled to the PSTN 130 after being disconnected from the PSTN130, thereby preventing the base station 115 from being used without theproper authorization after being relocated. Additionally, the basestation 115 preferably calls the service center 125 periodically, asdescribed in reference to step 445, even when the telephone interface245 has not been disconnected from the PSTN 130. The periodic calling ofthe service center 125 is intended to simply verify authorization when abase station 115 has not been relocated for a long period of time.

Referring next to FIG. 5, a flowchart depicts the operation of theservice center microprocessor 315 (FIG. 3). According to the presentinvention, the authorization function is begun when the telephone port305 provides a telephone signal to the DTMF device 310 in response to acall from a base station 115. The telephone signal, which preferablycomprises ANI information generated by the PSTN 130, is decoded by theDTMF device 310 and supplied, at step 505, to the microprocessor 315.The microprocessor 315 thereafter compares, at step 510, the ANIinformation to information stored in the database 325 (FIG. 3). Asdescribed above, the ANI information may comprise the telephone numberfrom which the base station 115 is calling. In this situation, thetelephone number is compared to a list of telephone numbers stored inthe database 325 to determine whether it is one of the listed telephonenumbers, which are telephone numbers within the exclusion zones.

Alternatively, the ANI information could simply comprise the telephoneexchange from which the base station 115 is calling, and the database325 could simply include a list of telephone exchanges indicative ofregions wherein the base station coverage area could overlap or beincluded in any of the exclusion zones. This method would have theadvantage of utilizing a much less cumbersome database 325 that wouldneed to be updated less often. However, because the telephone exchangeswould be unlikely to correspond exactly with the boundaries of theexclusion zones, the base stations 115 might easily be prevented fromcommunicating over the RF channels in some regions where interferencewith the microwave stations 105 would not occur. As a result, the use oftelephone exchanges, rather than telephone numbers, would lessefficiently utilize the available RF spectrum.

When, at step 515, the telephone number, or, alternatively, thetelephone exchange, included within the ANI information is not found inthe database 325 (FIG. 3), indicating that the base station 115 is notin an exclusion zone, the microprocessor 315 retrieves, at step 520, thefirst authorization code from the memory 320 and provides it to the DTMFdevice 310. The DTMF device 310 subsequently encodes the firstauthorization code into a first authorization signal for transmission tothe base station 115, in response to which the base station 115 isauthorized to communicate over the RF channel.

When, at step 515, the telephone number or telephone exchange includedin the ANI information is found in the database 325, the microprocessor315 provides, at step 525, the second authorization code to the DTMFdevice 310. Upon reception by the base station 115, the secondauthorization code prevents communication over the RF channel, therebypreventing interference with any of the microwave stations 105 (FIG. 1).

In this manner, subscribers to the RF communication system are allowedthe use of portable base stations 115, rather than the fixed basestations provided in prior art systems. As a result, a user can, whennecessary, move his assigned base station 115 to a different locationand communicate therefrom with portable handsets 120 as long as the basestation 115 has not been moved to a location within an exclusion zone.The use of the base stations 115 and service center 125 thereforeprovides a convenient way for subscribers to share an existing RFchannel without interfering with stations, such as the microwavestations 105, which also communicate over the RF channel.

FIG. 6 is a block diagram of a base station 600 in accordance with afirst alternate embodiment of the present invention. This base station600 is similar to the base station 115 described in reference to FIGS. 2and 4, but, rather than monitoring a telephone interface 605, the basestation 600 comprises monitoring and power switching circuitry 610 formonitoring A/C power provided thereto from an A/C power supply (notshown), which normally powers the base station 600, and for generating asignal when the A/C power is interrupted. Coupled to the monitoring andpower switching circuitry 610 is a backup battery 615 for supplyingpower to at least portions of the base station 600, such as a controller620, when the A/C power is interrupted. As in the base station 115 (FIG.2) according to the preferred embodiment, the controller 620 of the basestation 600 includes a CPU 622 for controlling the operation of the basestation 600, a RAM 625 for storing a disconnect flag, and a ROM 630 forstoring the telephone number of the service center 125 (FIG. 3), a"call-in" time value, and the first and second authorization codes.

Referring next to FIG. 7, a flowchart depicts the operation of thecontroller 620 included in the base station 600 in accordance with thefirst alternate embodiment of the present invention. Initially, at step705, the monitoring and power switching circuitry 610 monitors the A/Cpower, and the CPU 622 monitors time values provided thereto from aclock 624 (FIG. 6). When, at step 710, the A/C power is not interrupted,the CPU 622 references the RAM 625 to determine, at step 715, whetherthe disconnect flag has been set. When the disconnect flag is set,operation of the CPU 622 resumes at step 705. Otherwise, the CPU 622sets, at step 720, the disconnect flag in the RAM 625.

When, at step 710, the A/C power is interrupted, such as when the basestation 600 is being relocated, and, at step 725, the disconnect flag isset, the CPU 622 clears, at step 730, the disconnect flag. Subsequently,the CPU 622 retrieves, at step 735, the telephone number of the servicecenter 125 which is stored in the ROM 630. When, at step 710, the A/Cpower is interrupted, and, at step 725, the disconnect flag is not set,operation of the controller 622 resumes at step 705 unless, at step 745,the time value generated by the clock 624 is equivalent to the call-intime value stored in the ROM 630. In this case, the CPU 622 alsoretrieves, at step 735, the telephone number of the service center 125.

In accordance with this first alternate embodiment, further operation ofthe base station controller 622 proceeds similarly to that described insteps 455 through 490 of FIG. 4. In this manner, the base station 600places a call to the service center 125 when A/C power has beeninterrupted and subsequently restored or when a periodic time period hasexpired.

It will be appreciated by one of ordinary skill in the art thatcombinations of the above described embodiments can be implemented in abase station for use in the RF communication system. For example, if abase station includes the monitoring circuitry 250 (FIG. 2), themonitoring and power switching circuitry 610 (FIG. 6) and the backupbattery 615, the base station could be designed to place a call to theservice center 125 only when a telephone interface has been reconnectedto the PSTN 130 after being disconnected from the PSTN 130 and when A/Cpower has been restored after interruption. Because both the telephoneinterface and an A/C power outlet must be disconnected to relocate thebase station, the base station would reduce the number of unnecessarycalls to the service center 125 which might be placed, for instance,after a power outage or after telephone service interruptions.

A second alternate embodiment of the present invention is envisioned inwhich the portable handsets 120 comprise frequency scanning apparatusfor use in system such as a conventional CT-2 system. A base station 800in accordance with the second alternate embodiment is depicted in FIG.8. The base station 800 preferably comprises transceivers 805 whichinclude frequency control circuitry 810 of a type well known to one ofordinary skill in the art. A CPU 815 included in a base stationcontroller 820 provides frequency selection signals to the transceivers805 via a frequency selection bus 825 coupled between the transceivers805 and the CPU 815. The controller 820 further comprises RAM 825 forstoring a disconnect flag set by the CPU 815 and a ROM 830 for storing,in addition to the parameters described in reference to FIGS. 2 and 4,first and second frequencies associated, respectively, with the firstand second authorization codes stored in the ROM 830. Additionally, thecontroller 820 includes monitoring circuitry 835 for monitoring atelephone interface 840 and generating a signal when the telephoneinterface 840 is determined to be disconnected from the PSTN 130 (FIG.1).

FIG. 9 is a flowchart depicting the operation of the base stationcontroller 820 (FIG. 8). In accordance with the second alternateembodiment, the controller 820 proceeds as described in FIG. 4 until, atstep 900, the CPU 815 receives the decoded authorization signal anddetermines, at step 905, whether the decoded authorization signal isequivalent to the first or second authorization code. When the firstauthorization code is received, indicating that communication over theRF channel is allowed, the CPU 815 enables, at step 910, thetransceivers 805 for communication over the RF channel. This ispreferably accomplished when the CPU 815 references the ROM 830 todetermine the frequency associated with the first authorization code,and therefore associated with the RF channel, and then provides anappropriate frequency selection signal to the transceivers 805. When thesecond authorization code is received, the CPU enables, at step 915, thetransceivers 805 for communication on a different frequency associatedwith the second authorization code by providing a frequency selectionsignal indicative of the different frequency to the transceivers 805. Inresponse to reception of the frequency selection signal, the frequencycontrol circuitry 810 (FIG. 8) is adjusted to the frequency assigned bythe CPU 815 and communication with the portable handsets 120 isestablished over the assigned frequency.

In accordance with the second alternate embodiment, RF communicationbetween the base station 800 and portable handsets 120 is allowed evenwhen the base station 800 is located within an exclusion zone. However,when the base station is located in an exclusion zone, communication isestablished over an RF channel which is different from that used by themicrowave stations 105 (FIG. 1), thereby preventing interference withthe microwave stations 105. In this manner, the base station 800 may beconveniently utilized in all regions encompassed by the RF communicationsystem, and users of portable handsets 120 are not isolated fromcommunication with the base station 800 when the base station 800 islocated in an exclusion zone. This base station 800 and the portablehandsets 120 communicating therewith, however, may require moreexpensive and complex circuitry for implementation of the frequencycontrol circuitry 810 and the frequency scanning apparatus for use inthe portable handsets 120.

FIG. 10 is a block diagram of a base station 950 in accordance with athird alternate embodiment of the present invention. This base station950 includes in the ROM 952 a pre-programmed telephone number 954 whichis loaded when the base station 950 is purchased. The preprogrammedtelephone number 954 preferably corresponds to the telephone number fromwhich the base station 950 will place calls to a service center. In thisalternate embodiment, the base station 950 still calls the servicecenter after disconnection from the PSTN 130 or after expiration of atime period. However, when the base station 950 places the call, thepre-programmed telephone number 954, as well as the ANI information, isprovided to a service center. The service center then provides a firstauthorization code, which allows communication, to the base station 950when the pre-programmed telephone number 954 is equivalent to thetelephone number from which the base station 950 is calling.

Referring next to FIG. 11, a service center 960 according to the thirdalternate embodiment is depicted. The service center 960 is intended foruse with the base station 950 of FIG. 10. According to this alternateembodiment, the service center 960 does not include a database listingtelephone numbers or telephone exchanges included within exclusionzones. Instead, the service center 960 bases its authorization entirelyupon whether or not the pre-programmed telephone number 954 (FIG. 10)matches the telephone number provided in the ANI information. Thismethod has the advantage of allowing a much simpler service center 960which does not have to be updated periodically. Additionally, becausethe base station 950 can only be used at a single telephone number,stolen base stations 950 become inoperable. However, in this alternateembodiment, the base stations 950 cannot be relocated by a subscriberand the RF spectrum is less efficiently utilized.

In summary, the RF communication system according to the preferredembodiment of the present invention includes base stations which can beeasily and conveniently relocated by a subscriber. The base stationsshare an RF channel with stationary point-to-point communicationdevices, such as microwave stations, which communicate on the RF channelover predetermined geographic areas, termed "exclusion zones".Therefore, the base stations can communicate on the RF channel in anygeographic region, excepting the exclusion zones, without interferingwith the microwave stations. A service center included in the RFcommunication system controls the communication capabilities of the basestations, which are coupled to the service center by a telephone networkhaving ANI capabilities. According to the preferred embodiment of thepresent invention, the service center automatically receives from thetelephone network the telephone number from which a base station iscalling and determines therefrom whether the base station is located inan exclusion zone. The service center then authorizes the base stationfor RF communication over the RF channel when it is not located in anexclusion zone. A base station may therefore be relocated any number oftimes and continue to communicate over the RF channel unless it has beeninadvertently relocated to a region within an exclusion zone.

It may be appreciated by now that there has been provided a frequencysharing scheme for relocateable base stations that prevents interferencebetween users of two different communication systems sharing the same RFchannel.

What is claimed is:
 1. A base station, in a radio frequencycommunication system, capable of being relocated among a plurality ofgeographic regions for communicating over a radio frequency channel, thebase station sharing the radio frequency channel with stationarycommunication devices over predetermined geographic areas, wherein thebase station is capable of accessing a telephone network to communicatewith a service center which authorizes use of the radio frequencychannel by the base station, the base station comprising:a memory forstoring a first predetermined telephone number of the service center;accessing means, coupled to the memory, for calling the firstpredetermined telephone number over the telephone network and forreceiving in response thereto an authorization signal over the telephonenetwork indicating that authorization of radio frequency communicationover the radio frequency channel is allowed in response to the servicecenter determining that the base station is not located in one of thepredetermined geographic areas of the stationary communication devices,wherein the service center determines the location of the base stationbased upon a telephone number from which the base station places a callto the service center; and a transceiver coupled to the accessing meansfor transmitting and receiving communications over the radio frequencychannel in response to reception of the authorization signal.
 2. Thebase station according to claim 1, wherein the accessing meanscomprises:dialing means for dialing the first predetermined telephonenumber; and a controller coupled to the dialing means for determiningwhether the dialing means is coupled to the telephone network, whereinthe controller provides the first predetermined telephone number to thedialing means in response to determining that the dialing means has beencoupled to the telephone network subsequent to being disconnected fromthe telephone network.
 3. The base station according to claim 1, whereinthe accessing means comprises:dialing means for dialing the firstpredetermined telephone number; and monitoring means coupled to thedialing means for monitoring power provided thereto by a power supply,wherein the monitoring means provides the first predetermined telephonenumber to the dialing means in response to determining that the powerprovided by the power supply has been restored subsequent to beinginterrupted.
 4. The base station according to claim 1, wherein theaccessing means comprises:dialing means for dialing the firstpredetermined telephone number; and a controller coupled to the dialingmeans and the memory for providing the first predetermined telephonenumber to the dialing means.
 5. The base station according to claim 4,further comprising:a clock coupled to the controller for generating timevalues, wherein the controller provides the first predeterminedtelephone number to the dialing means in response to expiration of apredetermined amount of time.
 6. A service center for authorizing theuse of a radio frequency channel by at least one base station capable ofbeing relocated among a plurality of geographic regions, the at leastone base station sharing the radio frequency channel with stationarycommunication devices for communicating over predetermined geographicareas, the service center coupled to the at least one base station by atelephone network having automatic number identification (ANI)capabilities, the service center comprising:a telephone port forreceiving from the telephone network information indicative of at leasta portion of a telephone number from which the at least one base stationis calling when the at least one base station couples to the servicecenter; a database for storing information associated with thepredetermined geographic areas over which the stationary communicationdevices communicate; and a processor coupled to the telephone port andthe database for comparing the information indicative of at least aportion of the telephone number to the information stored in thedatabase to determine whether the at least one base station is locatedwithin any of the predetermined geographic areas, the processorproviding an authorization signal to the telephone port for transmissionover the telephone network when the at least one base station isdetermined not to be located within any of the predetermined geographicareas, wherein the authorization signal indicates that the at least onebase station is authorized for radio frequency communication over theradio frequency channel.
 7. The service center according to claim 6,wherein the information stored in the database comprises a listing oftelephone numbers located within the predetermined geographic areas. 8.The service center according to claim 6, wherein the information storedin the database comprises a listing of telephone exchange numberslocated within the predetermined geographic areas.